Battery-operated (i.e. active) tracking badges and tags often emit radio-frequency (RF) and other signals such as ultrasonic or infrared (IR) signals. These signals are used to precisely establish the real-time location of mobile assets and people to which the badges and tags are affixed.
Typical fire rates for IR are set at every 3 seconds on badges and 9 seconds for asset tags. RF signals are typically set at every 12 seconds on each type of badge. Firing rates can be preselected. Since some tags feature a motion sensor, the tag will go to “sleep” (fire less often to save on battery life) when there is no movement.
Recent asset tag batteries may last up to three years, depending on their preselected firing rate. Patient/personnel tags have a shorter battery life because they are in use and firing signals more frequently than asset tags, consequently, badge batteries typically last up to 18 months. In any event, however, battery-operated tracking tags have a fixed energy budget.
U.S. patent publication 2008/0218351 discloses an RFID tag conservation method and system for active multi-modal RFID tags, illuminator/tag/reader systems, circuit architecture and operational algorithms for battery power conservation that extends tag battery life from a typical 6 months to >5 years. The system is particularly useful in asset and person tracking/inventory systems where power conservation is critical. The tag is configured with a microprocessor operational instruction set algorithm, modifiable on the fly via RF or IR, to synchronize a periodic tag awaken/sense envelope that overlaps the illuminator trigger pulse cycle and puts the tag into deep power conservation sleep for N periods of illuminator cycles. When the tag sees an illuminator signal with a different ID, or no illuminator signal at all, it transmits that anomaly via RF to a reader. This means the object or person with which the tag is associated has been moved out of the original illuminator field of view, permitting near real-time investigation and tracking
The following U.S. patents are related to at least one embodiment of the invention: U.S. Pat. Nos. 6,154,139; 6,104,295; 5,027,314; 5,572,195; 5,548,637; 5,119,104; 5,017,7984; 4,906,853; 5,387,993; 5,355,222; 5,276,496; 5,131,019; 5,027,383; 4,868,859; 6,838,992 and 6,462,656.
The following U.S. patents are also related to at least one embodiment of the invention: U.S. Pat. Nos. 4,048,729; 4,392,132; 5,093,786; 5,379,213; 5,724,357; 6,021,119; 6,665,000; 7,277,671; 7,403,111; 7,599,703; 5,883,582; 5,929,777; 5,929,779; 6,069,557; 6,241,364; 7,042,337; 6,577,877; 7,005,965; 7,389,180; 7,746,820; 7,747,261; 6,788,199 and 7,079,009.
There are a number of drawbacks to the tag transmissions of the above-noted prior art relative to the amount of energy required to transmit over infrared carriers, particularly in relation to the much lower amount of energy required to transmit over radio frequency carriers. Systems in the past have used a badge or tag IR transmission containing a serial number in the process of identifying a badge to the system. The length of the IR transmission is a significant determiner of battery life for the badges and a significant component of the length of the IR transmission is the serial number of the badge. Short serial numbers require reuse of serial numbers sooner resulting in possible duplication of badge identities within a facility causing a compromise in the integrity of the whole system. Longer serial numbers solve this problem but seriously reduce battery life. Therefore a design that can reduce the length of the IR packet without giving up a long serial number is invaluable for maximizing battery life.